This invention relates in general to an apparatus and technique of validating coins used in coin operated machines.
Coin operated machines have many different techniques for validating the coins employed and for detecting slugs and non-valid coins. These techniques have been around for as long as there have been coin operated machines.
Two coin validating techniques that are relevant to this invention are those shown in the U.S. Pat. Nos. 3,870,137 issued Mar. 11, 1975 and 3,918,565 issued Nov. 11, 1975. These two related patents deal with techniques for identifying a moving coin with an electronic sensor which senses passage of a coin and responds with a signal whose frequency and amplitude provides information about the coin or slug. This information can then be compared with information stored in memory to determine whether or not the coin is a valid coin. One of the techniques employed in these patents is the use of two separate sensors, one operating at a higher frequency and one at a lower frequency, to respond to the coin as it passes through two sensors. The higher frequency interacts more or less with the skin or the outer portion of the coin and the lower frequency interacts with the entire coin.
Another coin sensing device which has been known in this art is described in U.S. Pat. No. 4,416,364 issued Nov. 22, 1983. It shows the use of a sensing coil in association with an oscillator circuit whose output parameters change as a function of the coin in position.
One of the major disadvantages of the technique for detecting a coin as it moves along is that the rate at which the coin moves through the sensor will limit the amount of information and the time span during which sensed information can be obtained. This limits the level of discrimination or sensitivity. Furthermore, there is the possibility of the coin bouncing through in such a fashion as to provide an inadequate and inaccurate sensor response.
In addition, there are certain types of installations, such as coin operated clothes washing and drying machines, which do not have the height necessary to permit the coin to roll under the influence of gravity for the required distance to effect the sensing results obtained by the known techniques.
Most importantly, in all these systems, there is a trade-off between sensitivity and time. More specifically, a trade-off has to be made between false positives and false negatives. Any reasonable system will at times accept an invalid coin (false positive) and at times will reject a valid coin (false negative). In any arrangement, a trade-off has to be made between keeping false positives low and false negatives low.
One of the major objects of this invention is to provide an arrangement which can provide both a lower false positive and a lower false negative result.
A related object of this invention is to achieve this improved validation trade-off with a system that will operate to identify and validate the coin in a time span that is acceptable to the user.
A further object of this invention is to provide such a system as can be adapted for use in a wide variety of coin operated machines particularly machines such as washing and drying machines which do not provide a substantial distance for coins to drop.
A further purpose of this invention is to provide a system which will permit adaptation and adjustment so that factors of sensitivity and discrimination with respect to a particular coin can be enhanced thereby decreasing the risk of a false acceptance (false positive) with respect to slugs or substitutes for the valid coin.
Definitions
The term "coin" is used herein to generally refer to any valid coin, token, invalid coin, counterfeit coin or slug. The more specific term will be used when a less general reference is meant.
Rest frequency and rest amplitude refer to the parameters of the oscillator signal when the oscillator is not coupled to a coin. The rest state of the oscillator is also called the normal state.
The term "set" as used herein includes the situation where there is only one member.
"Recognition Parameter" is used herein to refer to any one or more direct or indirect parameters of the output signal of an oscillator. The parameter may be signal frequency, signal amplitude, difference between measured signal frequency and a standard value frequency, difference between a measured signal amplitude and a standard signal amplitude or any other direct or processed signal value. The recognition parameter used in the embodiment described herein is a point in a processed amplitude vs. frequency plane.